[The relationship between the timing of the Korotokoff sound (QKd) and the serum thyroid hormone concentrations].

The interval between the onsets of the QRS complex and of the brachial Korotokoff sounds at the diastolic pressure was termed QKd and it was already known that QKd was shortend in hyperthyroidism and prolongad in hypothyroidism distinctly. In the present study, simultaneous measurements of QKd, serum thyroxine (T4) and triiodothyronine (T3) concentrations, free T4 index (FT4I) and free T3 index (FT3I) were undertaken and attempts were made to examine the possible correlation of QKd to these parameters of thyroid function in sera. The QKd values of 24 euthyroid subjects had a normal range of 190 to 230 msec., 10 patients with hypertyroidism had Qkd values ranging from 145 to 180 msec. and 9 hypothyroid patients had QKd values ranging from 230 to 305 msec. Plots of QKd agaist serum T4 and T3 concentrations denoted statistically significant inverse relations in the T4 and T3 concentrations denoted statistically significant inverse relation in the T4 and T3 concentrations approximately less than 20 mug/dl and 400 ng/dl respectively (4 = 0.59 and -0.62 respectively) and above these concentrations of T4 and T3, QKd was nearly constant at the level of 165 msec irrepective of T4 and T3 concentrations. The statistically significant inverse relations were also observed between QKd and FT4I and FT3I in the FT4I and FT3I values less than 18 and 280 respectively (r= -0.80 and -0.74 respectively) and above these values of FT4I and FT3I, QKd was remained constant. In 18 hyperthyroid subjects receiving antithyroid medication, QKd, FT4I and FT3I were measured. QKd values from the patients whose FT4I and/or FT3I were above normal were significantly shorter than the QKd from the patients with normal FT4I and ft3i (183 +/- 9.8 msec vs 211 +/- 19 msec, p less than 0.01). In 16 patients with primary hypothyroidism receiving L-thyroxine for replacement therapy more than 6 months of period, QKd, FT4I and FT3I were measured and TRH-test was performed. FT4I and FT3I in these patients were all in normal range and 8 out of 16 patients had normal response to TRH-test and others were of no response to TRH-test. No difference in QKd values was obtained between patients with normal response and with no response to TRH-Test. These results indicate that QKd is more closely related to serum free T4 and free T3 concentrations and the extent of prolongation of QKd in hypothyroidism reflects the decreased serum thyroid hormone concentrations, whereas the shortend QKd in hyperthyroidism does not parallel the increased serum thyroid hormone concentrations. QKd is useful index not only for the rapid assessment of thyroid function as proposed by previous investigaters, but also for the rpaid evaluation of efficacy of antithyroid drugs administered in hyperthyroidism.